With the development of computer technologies and network technologies, an amount of information tends to grow by geometric progression, data of human beings reaches an unprecedented scale, and storage and management of such super-large-scale data becomes a great challenge in the industry. When the super-large-scale data is stored and managed in a traditional centralized manner, a high-efficiency read/write operation cannot be provided, and high expansibility and high availability cannot be met. In such a background, various storage systems formed by multiple storage nodes have emerged.
In a storage system formed by multiple storage nodes, generally multiple copies of same data are stored to avoid data loss caused by a single-point failure; therefore, an urgent requirement of the system is to keep the number of data copies stable. In addition, as people's requirement for sustainable working of storage systems is quickly growing day after day, online capacity expansion of a distributed storage system becomes an indispensable part of basic functions of the system. Then how to issue a data recovery task in a case of system data damage becomes a focus of a current technology.